This invention relates in general to wheelchair suspension systems and more particularly, to resilient independent suspension members that have the ability to interact with one another to improve drive wheel traction.
Conventional wheelchairs include side frames and a seat assembly supported by the side frames. Drive wheels and front casters are attached to the side frame. The drive wheels may be driven by the wheelchair occupant or by an electrical motor. Anti-tip wheels are often provided rearward of the drive wheels. The anti-tip wheels are adapted to engage the ground to prevent the wheelchair from tipping over.
The drive wheels, casters, and anti-tip wheels of traditional wheelchairs are rigidly attached to the side frames. Rigidly attached wheels and casters typically fail to maintain contact with the ground as the wheelchair negotiates obstacles or irregular ground surfaces. Moreover, such wheels and casters provide an abrupt jolt to the wheelchair occupant as the wheels and casters engage the ground.
To overcome this problem, pivotal suspension members have been provided for supporting the wheels and casters. Such suspension members are adapted to pivot about a common transverse axis to permit the wheels to maintain contact with the ground. The suspension members may be spring-biased to absorb shock and provide greater comfort for the wheelchair occupant. In addition to absorbing shock, the spring-biased suspension members further insure that substantially all the wheels and casters maintain contact with the ground. Some suspension members provide variable rate resistance to movement. The resistance progressively increases as the suspension members move. The rate of resistance may increase non-linearly. It is well known to use elastomeric elements to bias suspension members. The elastomeric elements cooperate with the frame and suspension members to resist rotational movement of the suspension members.
While the advancements in suspension members have progressed towards maintaining ground contact, such advancements have limited application. Maintaining ground contact is still a problem when negotiating obstacles or irregular ground surfaces because of the passive movement of the suspension members. The passive movement has a limited effect on improving the traction of the drive wheels.
What is needed is a wheelchair suspension system that has suspension members interacting to positively urge the drive wheel suspension members into contact with the ground and thus improve the traction of the drive wheels.